The invention relates to a punch rivet with a cutting edge which is arranged on the end face of its rivet shank and is formed in the cutting region by an outer face extending parallel to the axis and a conical inner face of the rivet shank.
The invention also relates to a riveted joint produced with such a punch rivet, a tool suitable for this purpose and to a method of producing a riveted joint.
A punch rivet of the type described above is described and illustrated in DE-OS 43 33 052 and has, on its side remote from the cutting edge, that is its back, a plate-like countersunk head which closes the punch rivet with a plane lid on this side, the rim of the lid passing conically or in a rounded fashion into the outer face of the rivet shank on its side facing the cutting edge. The plane outer face of the lid is suitable for application of a ram during the riveting process which presses the punch rivet through the components to be riveted, the components facing the cutting edge, that is the upper components, being pierced by the punch rivet and the component remote from the cutting edge, that is the bottom component, receiving the cutting edge due to the effect of a cone which, as a projection of a die, is directed toward the hollow interior of the punch rivet and widens the cutting edge radially outwardly when the cutting edge penetrates the bottom component without the bottom component being pierced.
DE-PS 39 42 482 describes a similar design with a head which is rounded in the manner of a tallow-drop screw. The known design dealt with above is also disclosed in DE-OS 44 31 769 which explains the requirements of the punch rivet material, which are that the punch rivet must have the necessary hardness in the cutting edge region for punching through the upper components, but be highly deformable in the shank region in order to widen the rivet shank radially outwardly within the bottom component in the cutting edge region and therefore to effect riveting. The state of the art showing punch rivets with a covering head is extensive.
DE-PS 28 39 838 describes a fundamentally different design of a punch rivet which consists of a round, axially symmetrical, solid body terminated on both sides by a plane radial end face. The corner which is right-angled in cross section and with which the radial end faces pass into a relatively narrow cylindrical annular face serves as a cutting edge in this punch rivet. To rivet two superimposed metal sheets, the punch rivet is pressed through the sheets, the two sheets being punched without the punch rivet being deformed. Riveting is effected in that, after punching, the sheets are pressed together by the punch rivet held in the punched holes, are deformed radially inwardly owing to an indentation formed between the end faces of the punch rivet and penetrate into the indentation, the punch rivet being held by the sheets and securing them with its indentation. Apart from the fact that this punch rivet is based on a fundamentally different principle from the punch rivet described at the outset, as it is not deformed during production of a riveted joint, the known solid punch rivet with its indentation can exert only relatively low holding forces on the two superimposed sheets as the punch rivet allows only a relatively slight, radially inwardly directed deformation of the sheets into the indentation, so a riveted joint withstanding considerable forces cannot be produced with this known punch rivet.
Reference is finally made to a riveted joint which is disclosed in PCT specification WO 93/10925 and is based on the principle of pressing two superimposed sheets together with a ram into a die such that a common material eyelet with outward radial widening is produced without the sheets being punched. The ram attenuates the sheet material which expands radially in the process, an undercut in the die ensuring that one sheet is pressed into the undercut, the other sheet following this undercut and therefore being riveted to the other sheet. A sleeve which surrounds the ram and presses the sheets into the die with the ram can remain in the hollowed eyelet in order to stabilise it. The sleeve has, on its back, a narrow head which is obviously to increase the strength of the riveted joint. As the above-described riveted joint is based on the riveting of the two plates at the base of the passage, so that production of the riveted joint is not dependent on genuine punching of at least one sheet and pronounced deformation of the punch rivet, this known method of producing a riveted joint does not provide any starting point for the design of a punch rivet with which genuine punching and deformation of the punch rivet are effected during riveting.
It is an object of the invention to provide a punch rivet which has a particularly simple design eminently suitable for mass production and can advantageously be worked so as to produce stable, heavy-duty riveted joints.
The present invention provides a punch rivet with a cutting edge which is arranged on the end face of its rivet shank and is formed in the cutting region by an outer face extending parallel to the axis and a conical inner face of the rivet shank, characterised in that the outer face extends continuously parallel to the axis over the entire rivet shank and the punch rivet is provided with the same cutting edges on either side in an axially symmetrical design in the form of a tube.
The punch rivet according to the invention requires a smaller clinching force than a punch rivet having a lid-like head on the side remote from the cutting edge. This head prevents the respective side of the punch rivet from expanding when pressed onto the top component. For the punch rivet to act as a solid abutment with its head designed as a lid, it has to be pressed into the surface of the top component and this demands considerable forces. With the punch rivet according to the invention, on the other hand, which receives the punching pressure on its back, it is possible for the tubular punch rivet to expand radially on this side owing to the absence of a lid so it effectively claws in the top component and only has to be deformed by it to the extent of widening. Widening of the punch rivet on the side which receives the punching pressure is therefore particularly advantageous for processing of the punch rivet. During this widening of the back of the punch rivet, completely mutually adapted deformation of the respective part of the punch rivet and of the material of the top component occurs as the respective part of the punch rivet pushes the material of the top component forward to a certain extent during this deformation, producing an intimate connection between the respective part of the punch rivet and the top sheet metal part at this point. This considerably increases the strength of the riveted joint. The punch rivet is also distinguished in that, owing to its axially symmetrical design, its position does not have to be checked with respect to front and back, in particular during automatic supply to a processing station. During the riveting process, each side of the punch rivet can be used as its front, that is the side performing the punching process. This automatically also allows particularly simple production of the punch rivet as special features on either side do not have to be allowed for. Owing to its tubular symmetrical design, it can receive a punched out piece from either side. The design of the punch rivet with a cutting edge also on the back of the punch rivet where it is pressed against the components to be riveted by means of a tool affords the further advantage that the inner face which is also conical on this side of the punch rivet simplifies central introduction of a punching tool and simplifies the expansion thereof which occurs during the riveting process, owing to the material attenuation there. This part of the punch rivet is then placed on the material of the component to be riveted, smoothly with a uniform transition owing to the conicity of its inner face, without a special step being able to appear as it does not in fact exist.
The background publication xe2x80x9cStanznieten fxc3xcgt umformend ohne Umlochen der Blechexe2x80x9d (Bxc3xa4nder Bleche Rohre 4-1993, pages 46-55, FIG. 9), illustrating the punch riveting process with the punch rivets dealt with at the outset, shows the pronounced effect of a cover-like head which prevents widening of the punch rivet at its back. It can be seen that a considerable free space remains beneath the head of the respective punch rivet after punching so an intimate connection between the back of the punch rivet and the upper component cannot be made. As already mentioned, this is avoided with the punch rivet according to the invention owing to its radial widening capability, so the desired intimate connection between the widened part of the punch rivet and the upper component required for special strength is achieved.
Overall, therefore, the punch rivet according to the invention had a number of technically significant advantages which set it apart from the state of the art in a convincing and surprising manner.
A particularly simple embodiment of the punch rivet is produced if its outer face is continuously cylindrical in design. This configuration also simplifies automatic supply of the punch rivet which can be grasped, furthermore, by a conventionally designed tool and pressed into the components to be riveted. Clamping of such a punch rivet with conventional grippers affords the additional advantage that the punch rivet can be exactly grasped axially on its cylindrical outer face, guaranteeing exact location and orientation thereof for the punching of the components. The exact application of the punch rivet onto the top component and the beginning of punching are crucial for correct performance of the punching process and of the riveting process.
The rivet shank can be axially corrugated in cross section. As a result, the punch rivet is held non-rotatably by the components to be riveted, in other words the riveted components can receive a high, opposingly acting torque without the riveted joint being released.
An advantageous configuration of the rivet shank is achieved if it is designed as a continuous tube. This is particularly advantageous as it simplifies production of the punch rivet. However, it is also possible to arrange a radial wall in the rivet shank between the cutting edges. This interrupts the permeability of the pipe, which is important if the opposing sides of the respective components are also to be sealed by the punch rivet.
The rivet shank can be produced from a rolled sheet metal blank with an axial butt joint. The butt joint can be narrow in design but can also leave open a slot. In this case, material from the components which are to be riveted penetrates into the slot during riveting and this prevents the punch rivet and therefore the riveted joint from twisting.
To achieve a certain degree of radial imperviousness, however, the butt joint can also be formed with an overlap.
To prevent the rivet shank from being pressed apart in the region of the butt joint in the case of a punch rivet with a rivet shank consisting of a rolled sheet metal blank, in particular during the riveting of relatively hard materials, the butt joint can advantageously be bridged by fasteners. Such fasteners can consist of widening projections which are inserted into correspondingly shaped recesses, provided with undercuts, on the opposing side of the butt joint. The assembly of the projections with the recesses produces a rigid connection between the respective longitudinal sides of the rivet shank along the butt joint so the butt joint cannot be pressed apart when being driven into the materials to be riveted.
Another method of twist prevention involves interrupting the cutting edges with recesses. The material of the lower component is then pressed into these recesses as the punch rivet is pressed through so the riveted punch rivet cannot be twisted relative thereto. At its back, the material of the top component is also pressed into the respective recesses during widening of the cutting edge at the back of the punch rivet so twisting is also prevented here and prevents twisting of all the components. The overall quality of the riveted joint is increased by this complete prevention of twisting.
A riveted joint between at least two plate-like components can be produced using the above-described punch rivet, the upper components being punched by the punch rivet and the bottom component receiving the front cutting edge in widened form. The two cutting edges are radially widened to substantially the same extent such that the back cutting edge, that is the cutting edge remote from the front cutting edge, conically widens the punched hole in the top component and is positively riveted with this widening. The thus widened cutting edge represents the end of a conical widening of the rivet shank which therefore forms a rivet head which can be widened without particularly high pressure, as this widening is not prevented by transverse connections over the rivet shank of the type found in the case of known punch rivets with a lid-like head.
The piece punched from the upper component or components can be fastened in the rivet shank by axial compression. This is advantageous because, on the one hand, the two sides of the riveted joint are separated in an impervious manner, which prevents the penetration of sprayed water and the like in the car industry, for example, and, on the other hand, an uncompressed punched-out piece falls from the riveted joint and has to be disposed of somehow so it cannot obstruct subsequent operations in any way.
The riveted joint can be produced particularly advantageously if components made of aluminium sheet are to be riveted and the punch rivet consists of a precipitation-hardened aluminium which is harder than the aluminium sheet. In this case, the entire riveted joint including the components to be riveted consists of the same material which is, in particular, corrosion-resistant and is of particular importance in many cases where corrosion resistance and lightness are paramount.
It is known to use a die and a ram for producing the various riveted joints, the particular feature of the riveting tool used in this connection being that the die as well as the ram have a conical part which fits into the rivet shank and widens the respective cutting edge substantially to the same extent in each case. The conical parts converge with a blunt end to such an extent that these parts of die and ram produce the above-mentioned axial compression of a punched-out piece.
The method of producing the above-mentioned riveted joint is preferably carried out in that a punch rivet is pressed through one or more layers of components, the cutting edges being widened to substantially the same extent and on the one hand penetrating into the bottom component and on the other hand positively enlarging the top component. Riveting is therefore substantially symmetrical on both sides of the riveted joint, in other words the quality of riveting is virtually identical on both sides. The punched-out piece produced during pressing through can be pressed against the die by the relevant part of the ram such that the punched-out piece is fastened in the rivet shank by radial widening.